1. Field of the Invention
The present invention relates to a method and apparatus for detecting a thickness of a layer of powder on a surface.
2. Description of Related Art
There are many devices for detecting the thickness of a layer of material on a surface. However, many of these detectors are not satisfactory for measuring the thickness of a layer of a powder material.
For example, U.S. Pat. No. 1,909,652, issued to Bower, discloses a glazing thickness gauge that includes broad teeth 11 at each end thereof. As can be seen in FIG. 3, each of the broad teeth 11 are tapered at the tip thereof so as to form a point. In view of the fact that the supporting teeth 11 are at a point and not at a flat surface, the disclosed gauge may not necessarily be held perpendicular to the surface on which the layer is being measured. If the gauge is not reasonably perpendicular to the surface, the accuracy of the measurement will be jeopardized. In addition, the measuring blades 16, 17, are relatively broad in width. Accordingly, if the blades 16, 17, contact a powder material on the surface being measured, the blades 16, 17, will tend to plow the powder off to one side of the blades. As a result of this plowing effect, powder moved by one of the blades 16, 17, may spill over into the path of the other of the blades 16, 17, thus creating an inaccurate measurement. Thus, it can be seen that the Bower device is not satisfactory for accurately measuring the thickness of a powder layer.
Other devices, such as those disclosed by Japanese Laid-Open Patent Application Nos. 61-100601 and 60-127401, disclose measuring devices having broad measuring blades which would create the spill over affect discussed above with respect to the Bower device.
There are also several devices that have been disclosed that utilize rollers for measuring the thickness of deposits. One such device is disclosed in U.S. Pat. No. 2,839,835, issued to Zollinger. However, such roller devices do not result in accurate measurements because they either skid on the powder or they ride up on the powder surface like a boat hull, thus jeopardizing the accuracy of the measurements. In addition, the roller type devices are relatively bulky and are not convenient to carry.